Entryphone is a device installed at the entrance of a building to allow visitors to communicate with the occupants inside. It is also known as an intercom or buzzer system. An intercom refers to a two-way communication system used inside a building, while buzzer systems usually have a non-verbal signaling mechanism that allows visitors to alert occupants of their presence. Other synonyms for entryphone include access control system, doorphone, callbox, and door intercom. While the purpose of the device remains the same, the naming convention often depends on the technical specifications, features, and brand names.